The actors have two adopted children, five-year-old Connor and Isabella, eight. It is understood that no arrangements have yet been finalised regarding custody but it is thought they will share the responsibility. The couple did not say whether the split would lead to a divorce.

A spokesman for the actors, Pat Kingsley, said: "Citing the difficulties inherent in divergent careers, which constantly keep them apart, they concluded that an amicable separation seems best for both of them at this time." The couple had made the decision "regretfully".

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In a 1998 interview, Kidman said: "It's been nine years and I'm past the seven-year itch. When you're loved for your flaws, that's when you really feel safe." The couple met while making the film Days of Thunder and have subsequently starred together in Far and Away and the sexually explicit Eyes Wide Shut, in which they played married psychologists caught in a web of envy and obsession.

Cruise, 38, star of Born on the Fourth of July, The Color of Money, Mission: Impossible and Top Gun, commands more than $20 million (£14 million) a film and is arguably the most powerful film star in the world. He is currently filming with Penelope Cruz, the beautiful co-star of his latest movie, Vanilla Sky.

Kidman, a 33-year-old Australian, has starred in Batman Forever, Malice and To Die For. She attracted worldwide attention in 1998 for her role in The Blue Room at the Donmar Warehouse directed by Sam Mendes - a performance described as "pure theatrical Viagra" by The Daily Telegraph's critic Charles Spencer.

Yesterday's announcement came as it emerged that Kidman was dropping out of David Fincher's The Panic Room two weeks into filming because of a knee injury. She will be replaced by Jodie Foster.

The couple, both members of the Church of Scientology, have spent much of the past four years living in England. In October 1999 they spent a reported £2 million on a nine-bedroom house in Dulwich, south London. They also have homes in the US and Australia. Cruise was previously married for three years to the actress Mimi Rogers.